Project Summary/Abstract Carbon monoxide (CO) is of intense current interest as a potential therapeutic to improve human health. This is due to pre-clinical studies that have demonstrated the beneficial health effects of this gaseous molecule, including its dose-dependent anti-hypertensive, anti-inflammatory and cell protective effects. To date, studies of the biological effects of CO have been performed almost exclusively using variable concentrations of CO gas or metal carbonyl-based CO-releasing molecules (CORMs). These approaches have limitations in terms of control over the timing, location and amount of CO released. To address the need for the delivery of precise amounts of CO, particularly for studies of the dose-dependent biological effects of this molecule, compounds that release CO only upon exposure to light (photoCORMs) are being developed. The central hypothesis being tested in this project is that an extended flavonol-based structural framework can be used to develop a novel family of visible light-induced CO-releasing molecules that can deliver CO in a highly controlled manner. Preliminary studies demonstrate that the flavonol framework can be tuned in terms of its light absorption properties and CO release efficiencies. The flavonol-based structural motif also offers the opportunity for functionalization to add appendages for expanding the potential biological applications of the compounds. These preliminary results provide a strong rationale for further studies of extended flavonols as chemical tools for CO delivery. The specific aims of this study are to: 1) develop visible light-induced CO- releasing molecules based on an extended flavonol framework that exhibit absorption features at >500 nm, display high efficiency for CO release, function in both aerobic and anaerobic environments, and are defined in terms of their antioxidant and toxicity properties; 2) develop fluorescent probes for CO that can replace the CO consumed during detection and can be monitored during both the CO detection and release processes, and 3) develop CO-releasing molecules that are targeted to mitochondria. Each specific aim involves a combination of synthetic, photochemical, toxicity, and fluorescence microscopy investigations. Completion of the proposed studies will provide a new family of versatile chemical tools for CO delivery with potential applications in biological systems.